Tham khảo tài liệu 'mechanical properties of engineered materials 2008 part 2', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 1 Overview of Crystal Defect Structure and Mechanical Properties and Behavior INTRODUCTION The mechanical behavior of materials describes the response of materials to mechanical loads or deformation. The response can be understood in terms of the basic effects of mechanical loads on defects or atomic motion. A simple understanding of atomic and defect structure is therefore an essential prerequisite to the development of a fundamental understanding of the mechanical behavior of materials. A brief introduction to the structure of materials will be presented in this chapter. The treatment is intended to serve as an introduction to those with a limited prior background in the principles of materials science. The better prepared reader may therefore choose to skim this chapter. ATOMIC STRUCTURE In ancient Greece Democritus postulated that atoms are the building blocks from which all materials are made. This was generally accepted by philosophers and scientists without proof for centuries. However although the small size of the atoms was such that they could not be viewed directly with the available instruments Avogadro in the 16th century was able to determine that one mole of an element consists of X 1023 atoms. The peri- Copyright 2003 Marcel Dekker Inc. odic table of elements was also developed in the 19th century before the imaging of crystal structure was made possible after the development of x-ray techniques later that century. For the first time scientists were able to view the effects of atoms that had been postulated by the ancients. A clear picture of atomic structure soon emerged as a number of dedicated scientists studied the atomic structure of different types of materials. First it became apparent that in many materials the atoms can be grouped into unit cells or building blocks that are somewhat akin to the pieces in a Lego set. These building blocks are often called crystals. However there are many materials in which no clear grouping of .
